In the art of papermaking, an aqueous suspension containing cellulosic fibres, and optional fillers and additives, referred to as stock, is fed through pumps, screens and cleaners, which subject the stock to high shear forces, into a headbox which ejects the stock onto a forming wire. Water is drained from the stock through the forming wire so that a wet web of paper is formed on the wire, and the web is further dewatered and dried in the drying section of the paper machine. Drainage and retention aids are conventionally introduced at different points in the flow of stock in order to facilitate drainage and increase adsorption of fine particles such as fine fibres, fillers and additives onto the cellulose fibres so that they are retained with the fibres on the wire. Examples of conventionally used drainage and retention aids include organic polymers, inorganic materials, and combinations thereof.
U.S. Pat. No. 6,103,065 discloses a method for improving the retention and drainage of papermaking furnish comprising the steps of adding at least one cationic high charge density polymer of molecular weight 100,000 to 2,000,000 to said furnish after the last point of high shear; adding at least one polymer having a molecular weight greater than 2,000,000; and adding a swellable bentonite clay.
EP 1 238 161 B1 discloses a process for making paper or paper board in which a cellulosic suspension is flocculated by addition to a thin stock stream of the cellulosic suspension of a substantially water-soluble cationic synthetic polymer of intrinsic viscosity of at least 4 dl/g, wherein the flocculated cellulosic suspension is subjected to mechanical shearing and then reflocculated by addition subsequent to the centri-screen of a reflocculating system comprising (i) a siliceous material and (ii) a substantially water soluble anionic polymer of intrinsic viscosity of at least 4 d/g. The process is claimed to provide improvements in retention and drainage.
WO 2004/015200 discloses a method for producing paper and board by shearing the paper material, adding a microparticle system made of cationic polymers and a fine-particle inorganic component to the paper material following the last shearing step before agglomerating the material, dewatering the paper material so as to form sheets, and drying said sheets. The method is claimed to provide improvements in retention and drainage.
It would be advantageous to be able to provide a papermaking process with further improvements in drainage, retention and formation.